Method of operating an electric machine having an integrated coolant level sensor

ABSTRACT

A method of operating an electric machine includes flowing a coolant into an interior portion of a housing of the electric machine, and sensing a level of coolant in a coolant collection area within the interior portion with a coolant level sensor arranged at the housing.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional of U.S. application Ser. No. 13/007,243filed Jan. 14, 2011, the disclosure of which is incorporated byreference herein in its entirety.

BACKGROUND OF THE INVENTION

Exemplary embodiments pertain to the art of electric machines and, moreparticularly, to a method of operating an electric machine having anintegrated coolant level sensor.

Electric machines produce work from electrical energy passing through astator to induce an electro-motive force in a rotor. The electro-motiveforce creates a rotational force at the rotor. The rotation of the rotoris used to power various external devices. Of course, electric machinescan also be employed to produce electricity from a work input. In eithercase, electric machines are currently producing greater outputs athigher speeds and are being designed in smaller packages. The higherpower densities and speeds often result in harsh operating conditionssuch as high internal temperatures, vibration and the like. Accordingly,many conventional electric machines include coolant systems that areconfigured to lower temperatures of internal components.

Coolant systems include airflow systems, water based coolant systems,oil based coolant systems and glycol based coolant systems. Airflowsystems typically include fans that direct a convective airflow throughthe electric machine. Water based coolant systems typically circulatewater through a jacket that extends about the electric machine. Oilbased systems introduce oil or other forms of coolant directly into theelectric machine. The coolant flows onto, for example, stator windingsand collects in a lower portion of the machine. The coolant is thendirected to a heat exchange member. The heat exchange member extractsentrained heat from the coolant. The coolant is then passed back throughthe electric machine.

BRIEF DESCRIPTION OF THE INVENTION

Disclosed is a method of operating an electric machine including flowinga coolant into an interior portion of a housing of the electric machine,and sensing a level of coolant in a coolant collection area within theinterior portion with a coolant level sensor arranged at the housing.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way.With reference to the accompanying drawings, like elements are numberedalike:

FIG. 1 depicts an electric machine including an integrated coolant levelsensor in accordance with an exemplary embodiment; and

FIG. 2 depicts an electric machine including an integrated coolant levelsensor in accordance with another aspect of the exemplary embodiment.

DETAILED DESCRIPTION OF THE INVENTION

A detailed description of one or more embodiments of the disclosedapparatus and method are presented herein by way of exemplification andnot limitation with reference to the Figures.

Exemplary embodiments provide a coolant level sensor that is integrateddirectly into an electric machine. The coolant level sensor ispositioned at a lower portion of a machine housing in an area withinwhich collects coolant. The coolant sensor provides feedback to acontroller indicating a level of coolant in the electric machine. Basedon the level of coolant, the controller adjusts coolant flow into theelectric machine. In this manner, the controller ensures that coolantdoes not rise to a level that might interfere with moving components inthe electric machine. More specifically, coolant interfering with movingcomponents or entering an air gap between moving and stationarycomponents could result in a substantial reduction in operationalefficiency. In addition, exposure to moving components could result in abreak down of the coolant, or the coolant could be caused to changestates, or air could be introduced into the coolant. Introduction of aircould cause the coolant to foam and lose any heat carrying capacity orsuffer a degradation of lubrication capability for bearings, gears, andthe like.

An electric machine in accordance with an exemplary embodiment isindicated generally at 2 in the figure. Electric machine 2 includes ahousing 4 having first and second side walls 6 and 7 that are joined bya first end wall 8 and a second end wall or cover 10 to collectivelydefine an interior portion 12. First side wall 6 includes an innersurface 16 and second side wall 7 includes an inner surface 17. At thispoint it should be understood that housing 4 could also be constructedto include a single side wall having a continuous inner surface. Inaddition, first end wall 8 includes an inner surface 20 and second endwall 10 includes an inner surface 22. Electric machine 2 is furthershown to include a stator 24 arranged at inner surfaces 16 and 17 offirst and second side walls 6 and 7. Stator 24 includes a body 28,having a first end portion 29 that extends to a second end portion 30,which supports a plurality of windings 36. Windings 36 include a firstend turn portion 40 and a second end turn portion 41.

Electric machine 2 is also shown to include a shaft 54 rotatablysupported within housing 4. Shaft 54 includes a first end 56 thatextends to a second end 57 through an intermediate portion 59. First end56 is rotatably supported relative to second end wall 10 through a firstbearing 63 and second end 57 is rotatably supported relative to firstend wall 8 through a second bearing 64. Shaft 54 supports a rotorassembly 70 that is rotatably mounted within housing 4. Rotor assembly70 includes a hub 74 that is fixed relative to intermediate portion 59,and a rotor lamination assembly 79. Rotor lamination assembly 79includes a plurality of laminations 84 that are stacked and aligned todefine an outer diametric surface 87. In the exemplary embodiment shown,rotor lamination assembly 79 also includes a series of permanent magnets90 embedded within laminations 84. As such, electric machine 2 takes theform of a permanent magnet electric machine. However, it should beunderstood that the electric machine in accordance with the exemplaryembodiment could take on a variety of forms.

Electric machine 2 is electrically connected to a motor control panel 97through a power cable 99 that includes a plurality of power conductors,one of which is indicated at 104, that electrically couple stator 24with a power source 108 having terminals (not shown) arranged in motorcontrol panel 97. Motor control panel 97 also houses a controller 114,having a memory 115, that may be employed to control motor starting,motor speed, and/or motor shut down, as well as various other operatingparameters as will be discussed more fully below. In the exemplaryembodiment shown, controller 114 is linked to a coolant system 120 thatdelivers a coolant 124, such as mixtures containing oil through housing4. By “through” it should be understood that coolant system 120 can notonly be configured to direct a flow of coolant directly into housing 4and/or onto first and second bearings 63 and 64, but may also beconfigured to direct a flow of coolant onto first and second end turnportions 40 and 41 of stator 24. Coolant 124 enters housing 4 through aninlet (not shown) provided on, for example, side wall 6 and exitshousing 4 through an outlet (also not shown) provided on side wall 7. Assuch, during operation, coolant 124 collects in a coolant collectionzone or area 126 at lower portion (not separately labeled) of interiorportion 12.

In accordance with an exemplary embodiment, electric machine 2 includesa coolant level sensor 130, which, in the exemplary embodiment shown, ismounted to inner surface 20 of second end wall 8. More specifically,coolant level sensor 130 is mounted in the lower portion of interiorportion 12 at coolant collection area 126. In accordance with one aspectof the exemplary embodiment, coolant level sensor 130 takes the form ofa capacitive sensor 135 having a sensing surface 138 that directlysenses a level of coolant in coolant collection area 126. Capacitivesensor 135 provides a signal to controller 114 through a sensing line137 that is representative of the level of coolant 124 in coolantcollection area 126. More specifically, as coolant 124 rises in coolantcollection area 126 moving along sensing surface 138, a capacitance ofcapacitive sensor 124 changes. The change in capacitance leads to achange in voltage/current that is passed to controller 114. The changein voltage/current is compared to data in a look up table stored inmemory 115 and correlated to a level of coolant 124 in coolantcollection area 126. In accordance with another aspect of the exemplaryembodiment illustrated in FIG. 2, wherein like reference numbers referto corresponding parts in the respective views, electric machine 2 isshown to include a coolant level sensor 160 mounted to an outer surfaceof first end wall 8 at coolant collection area 126. Coolant level sensor160 takes the form of a capacitive sensor having a sensing surface 165that detects the level of coolant in coolant collection area 126 withoutbeing directly exposed to the coolant. Of course, it should beunderstood that other forms of sensors could also be employed.

In this manner, controller 114 can then control coolant delivery inelectric machine 2 based on coolant level in coolant collection area126. Adjusting coolant flow ensures that coolant 124 does not rise to alevel that would reach moving components in interior portion 12. Inaddition to controlling coolant flow, controller 114 provides an alarmand may be configured to initiate an electric machine shut down if thecoolant rises above or falls below a predetermined level in interiorportion 12. As such, coolant level sensor 130 also provides anindication of any clogs or flow restrictions that may exist at orupstream from the coolant inlet or downstream from the coolant outlet.In this manner, coolant level sensor 130, in conjunction with controller114, enhances an overall operational life of electric machine 2. Morespecifically, controller 114 ensures that not only are the internalcomponents properly lubricated and allowed to rotate withoutrestriction, but the addition of coolant level sensor ensures that thecoolant is not subjected to forces that may lead to premature breakdownor that the electric machine is not operated with an excess of coolantthat could degrade operation.

While the invention has been described with reference to an exemplaryembodiment or embodiments, it will be understood by those skilled in theart that various changes may be made and equivalents may be substitutedfor elements thereof without departing from the scope of the invention.In addition, many modifications may be made to adapt a particularsituation or material to the teachings of the invention withoutdeparting from the essential scope thereof. Therefore, it is intendedthat the invention not be limited to the particular embodiment disclosedas the best mode contemplated for carrying out this invention, but thatthe invention will include all embodiments falling within the scope ofthe claims.

What is claimed is:
 1. A method of operating an electric machine, themethod comprising: flowing a coolant into an interior portion of ahousing of the electric machine; and sensing a level of coolant in acoolant collection area within the interior portion with a coolant levelsensor mounted to a wall of the housing.
 2. The method of claim 1,further comprising: sending a signal indicating a level of coolant inthe coolant collection area from the coolant level sensor to acontroller.
 3. The method of claim 1, further comprising: controllingthe flow of coolant based on the level of coolant in the coolantcollection area.
 4. The method of claim 1, further comprising: signalingan alarm if the coolant in the coolant collection area rises above apredetermined level.
 5. The method of claim 4, further comprising:initiating an electric machine shut down if the coolant in the coolantcollection area rises above the predetermined level.
 6. The method ofclaim 1, wherein sensing a level of coolant in the coolant collectionarea includes sensing a change in capacitance of the coolant levelsensor.
 7. The method of claim 1, further comprising: signaling an alarmif the coolant in the coolant collection area falls below apredetermined level.
 8. The method of claim 7, further comprising:shutting down the electric machine if the level of coolant in thecoolant collection area falls below the predetermined level.
 9. Themethod of claim 1, wherein sensing the level of coolant in a coolantcollection area includes directly sensing a level of coolant with acoolant level sensor mounted in the housing.
 10. The method of claim 1,wherein sensing a level of coolant in a coolant collection areacomprises sensing the level of coolant through a wall of the housing.11. The method of claim 1, further comprising: ceasing the flow ofcoolant if the level of coolant in the coolant collection area contactsmoving components of the electric machine.